1. Roasting
the tomatoes on a griddle: line
a griddle or heavy skillet with
aluminum foil and heat over medium
heat. Lay the tomatoes on the foil
and roast, turning several times,
until blistered, blackened, and
softened, about 10 minutes.
2. Roasting
the tomatoes in a broiler: lay
the tomatoes on a baking sheet
and place about 4 inches below
a very hot broiler. Roast until
blistered and blackened on one
side. Flip the tomatoes and roast
the other side. Cool and peel,
collecting any juices with
the tomatoes. Coarsely purée
tomatoes and juices in a food
processor or blender.
3. In a medium-size saucepan, heat the oil over medium heat. Add the onion and fry until deep golden, about 8 minutes. Add the tomatoes and chopped chile and simmer 15 minutes or so, stirring often, until reduced but not dry. Season to taste with lime juice, cilantro, and salt.